1. Field of the Invention
The present invention relates to a method of measuring front and back surfaces of a target object. For instance, the method according to an aspect of the invention relates to a method of measuring a front surface profile and a back surface profile of a lens.
2. Description of Related Art
When lenses are manufactured through transfer using metal molds, the optical axis of front surfaces of the manufactured lenses may be misaligned with the optical axis of back surfaces of the manufactured lenses, depending on precision and displacement of the metal molds. Such misalignment may hamper achievement of desired optical characteristics.
In view of the above, various proposals have been made on methods of measuring profiles of front and back surfaces of lenses.
For instance, a document 1 (JP-A-2006-78398) discloses a method and a device of measuring eccentricity and inclination of front and back surfaces.
According to the document 1, a target object-holding jig is used, and a lens (target object) and three reference balls are disposed on the target object-holding jig such that the lens and the three reference balls are exposed to front and back surfaces of the target object-holding jig. Three-dimensional profile data of the lens and coordinates of the centers of the reference balls are measured at the front and back surfaces of the target object-holding jig. Then, based on the coordinates of the center of the reference balls, three-dimensional profile data of front and back surfaces of the lens is synthesized, so that eccentricity and inclination between the front surface and the back surface of the lens are obtained from the synthesized data about the front and back surfaces of the lens.
However, since the above-described method requires high-precision balls to be used as the reference balls, preparation of the jig tends to incur high cost.
In addition, the coordinates of the centers of the reference balls are calculated by partially measuring the exposed potions of the reference balls, which may lead to measurement errors.